So all 5 of my females in the 10 gallon tank I have them in are looking great. I changed their water yesterday with adding aquarium salt and stress coat. I noticed today that one female out of no where lost part of her anal fin. I am still in shock of how it was taken off. I have a total of 6 betta females. 3 crowntails and 3 veiltails. I have one veiltail in a 1.5 gallon tank that I am using for her because she is healing from fin rot which I caught in time. My question is was my crowntail, Hoto (short for Heart of the Ocean), nipped at by the other females well one female is the aggressive one sometimes and that is Ruby, veiltail, or Do bettas just lose a chunk of their anal fins out of no where?

It looks like she got a nice little nip to the anal fin from one of the other girls. Probably since you just recently removed one they had a couple of little spats as they re-established their pecking order a little, and thats where your little girl there got a chunk taken out of her fins.
I wouldn't worry too much about it. It should heal up just fine on its own.

Quick question though. Why did you add salt? Unless you're treating multiple fish for something like ich or velvet, its best not to add salt into your larger, cycled tank as prolonged exposure can be harmful to your fish and you run the risk of crashing your cycle by doing a 100% water change to remove it.

Well I put that girl (above) in the 1.5 gallon with the other girl who is also healing. I added salt because a few of the other girls have some minor nicks on their fins nothing serious. I put the serious ones in the 1.5 gallon tank which is only 2 so far. I have had my females for a month and no problems yet except for the nipping but I was just shocked because the only one female I have that is aggressive as the dominate is Ruby and she hasn't nipped at any of the other females since putting them together but I guess because Hoto (above) is new that she nipped her to distinguish that she is alpha.

Well its always important to remember that with a group of female bettas of this strain they are still bettas and are still technically 'fighting fish'. They are aggressive, and while they will tolerate each other in the right conditions, you are still always going to see some kind of aggression or nipping, especially when you move or change anything.
Also, bettas are very unpredictable. Even in perfect conditions you can have a successful sorority going for months...and then one day have a disaster because on girl suddenly didn't like this other girl for some reason. Sororities are fun, and if done right you usually won't have any serious problems, but there is always that risk.

...Okay, so you have two females in a 1.5 gallon tank together? Thats just a recipe for disaster here, you need to remove one of the girls ASAP. Two girls together, especially in such a small space, is going to end with one or both of them severely injured or dead. There is a reason its best to keep females in larger groups, and there is really no exception to this rule with this species.

Go ahead and do another water-only 50% partial change on your 10 gallon to remove some of the salt in there, rearrange the tank(and remove all your girls if you can)and add the nipped girl you removed back in. Do a couple more water only 50% changes over the nest few days to remove s much of the salt you already added as you can and then just leave things be.....there is no use in treating healthy girls in a sorority with a few nips with salt. Stress coat is fine to add if you really want to add something, but clean, warm water is what is going to help heal the nips the best.

And yes, if you get another 10 gallon tank, provided whatever you have your current 10 on can handle the weight if you're setting them on the same thing, you can put them right next to each other.

IMO there is no need to QT anyone due to nipped fins. Now if you see blood or an infection that's obviously different. I've had females with fin nips like yours or worse, I left them in the community tank, did my regular 50% weekly water change & they healed up just fine, new growth could be seen within a few days. They can't work anyting out if they keep getting removed, just my opinion.